On some platforms, such as microcontrollers with a single-precision
FPU, operations on double type can be significantly slower compared
to the float type. For example, on ESP32-S3 microcontroller, decoding
a QR code of a certain size may take 1700ms when 'double' is used and
just 250ms when 'float' is used.
This commit adds two options to allow for such optimizations:
- QUIRC_FLOAT_TYPE: if defined, it is the type name to use in floating
point calculations. Can be set, for example, using:
CFLAGS += -DQUIRC_FLOAT_TYPE=float
- QUIRC_USE_TGMATH: if defined, Quirc will internally use <tgmath.h>
header, instead of <math.h>. This C99-or-later header allows the
program to call type-generic functions, such as 'sqrt', and the
calls will be dispatched to the correct implementation (sqrtf, sqrt,
sqrtl) depending on the actual argument type. Without setting this
option, the benefit of -DQUIRC_FLOAT_TYPE=float would be limited as
the double-precision versions of math functions would still be used.
The change is backwards compatible with existing applications. If
these macros are not defined, the behavior is the same as before.
* Make flood filling logic iterative (vs recursive)
I basically tried one-to-one conversions here to avoid mistakes.
probably it has a room for later optimizations.
* Use explicit malloc (vs variables on stack) to allocate the work area.
* Estimate the amount of memory for the work area dynamically
from the image size, instead of using a constant FLOOD_FILL_MAX_DEPTH,
which is too big in the most cases.
Fix#2, this patch makes large images support a compile time option by
allowing QUIRC_MAX_REGIONS to be tuned via CFLAGS up to 65534 (current
default is 254).
